Assume that equilibrium GDP (Y) is 5,000. Consumption (C) is given by the equation C = 500 + 0.6(Y - T). Taxes (T) are equal to 600. Government spending is equal to 1,000. Investment is given by the equation I = 2,160 - 100r, where r is the real interest rate in percent. In this case, the equilibrium real interest rate is: (Please Explain)